1. Technical Field of the Invention
The present invention relates to a cell thickness detection method for detecting a cell thickness of a liquid crystal panel, a cell thickness control system, and a manufacturing method for a liquid crystal device.
2. Description of the Related Art
Conventionally, liquid crystal displays include liquid crystal display panels constructed by laminating two substrates with a sealing member therebetween and injecting a liquid crystal into a space surrounded by the sealing member. In such liquid crystal display panels, a gap between the two substrates, which will be referred to as xe2x80x9ccell thicknessxe2x80x9d in the following description, is an important parameter that determines the thickness of a liquid crystal layer. Optical characteristics of the liquid crystal display panels are determined by the cell thicknesses thereof.
Normally, in a manufacturing process of a liquid crystal display device, two substrates are laminated with an uncured sealing member therebetween, and then the laminate is compressed with a predetermined pressure so that the substrates are bonded to each other. In this process, spherical or columnar spacers are mixed in the sealing member or spread over one of the substrates before laminating the other one thereon, so that the cell thickness is limited by the outside size of the spacers. The sealing member is then cured in this state by a heating process, etc., and a cell structure, that is, an empty cell, of the liquid crystal display panel is formed.
The above-described sealing member is provided with an opening which serves as an inlet for a liquid crystal, and the liquid crystal is injected into the above-described empty cell through this inlet. When the liquid crystal is injected, the liquid crystal display panel slightly deforms to swell outwards. Thus, during a sealing process of the liquid crystal in which a sealing material is applied to the inlet for the liquid crystal and is cured by applying ultraviolet rays, etc., the liquid crystal display panel should be compressed and the cell thickness is made uniform. When the liquid crystal is sealed as described above, the shape of the liquid crystal display panel at the sealing process is maintained, and the cell thickness can be made uniform over the entire display region.
Accordingly, the resulting cell thickness and the cell thickness distribution of the liquid crystal display panel are determined by the cell thickness thereof during the sealing process of the liquid crystal. Thus, conventionally, in the sealing process of the liquid crystal, the cell thickness is measured while the liquid crystal display panel is compressed, and the liquid crystal is sealed when the cell thickness becomes a desired value. With respect to measuring methods of the cell thickness, such a method is known in which light is emitted from a light source and interference of reflected light from the substrate surfaces, etc., is used for determining the cell thickness (a method using an optical thickness gauge which utilizes light interference). In addition, another method is also known in which a pair of polarizers are disposed in the front and rear of the liquid crystal display panel, and the hue of light transmitted through the liquid crystal display panel and the polarizers is used for determining the cell thickness.
However, the method in which the cell thickness is determined by utilizing the interference of the reflected light has the following problem. Since multiple layers such as a transparent electrode, an insulating film, an alignment film, a color filter, etc., are included in the liquid crystal display panel, the reflected light, which is generated at interfaces of the layers, causes interference, and the interference thereof becomes complex. In addition, the intensity of the reflected light is considerably small, so that it is difficult to determine the cell thickness with high accuracy.
In addition, there is also a problem in the method in which the cell thickness is determined by obtaining the hue of light transmitted through the liquid crystal display panel and the polarizers disposed in the front and rear of the liquid crystal display panel. When the cell thickness of a color liquid crystal display panel including a color filter is determined, the detected cell thickness is affected by the hue of the color filter. Thus, the detection of the cell thickness may not be possible due to the color filter. In addition, even if the detected value is corrected in consideration of the hue of the color filter, the cell thickness cannot be detected with sufficient accuracy.
Accordingly, an object of the present invention is to provide a new cell thickness detection method which is free from the above-described problems, and with which the cell thickness of a liquid crystal panel is detected with high accuracy without being affected by the existence of a color filter. In addition, it is also an object of the present invention to form a cell structure with high accuracy by using the new cell thickness detection method to provide a high quality liquid crystal device.
According to the present invention, a cell thickness detection method for detecting a cell thickness of a liquid crystal panel which is constructed by laminating two substrates and disposing a liquid crystal layer between the substrates includes the steps of setting a light path for transmitting light through a first polarizing means, the liquid crystal layer, and a second polarizing means, in that order; obtaining a spectrum of light which is transmitted along the light path; deriving a detection value which is a wavelength, a frequency, or other value related to the wavelength or the frequency at which the spectrum has a minimum or maximum value; and determining the cell thickness based on the detection value.
Accordingly, the spectrum of light which is transmitted through the first polarizing means, the liquid crystal layer, and the second polarizing means, in that order, is obtained. This spectrum includes the minimum or maximum value at a wavelength or frequency position that is determined by a relative angle xcfx86 between the polarization transmission axes of the first and second polarizing means, an optical anisotropy xcex94n and a twist angle xcex8 of the liquid crystal, and the cell thickness d. When the relative angle xcfx86 is set to a predetermined value, the wavelength or the frequency, at which the spectrum has the minimum or maximum value, vary with the cell thickness d without being affected by the hue generated by a color filter included in the liquid crystal panel, etc. Accordingly, by obtaining the wavelength, the frequency, or other value related to the wavelength or the frequency as the detection value, the cell thickness d can be determined with high accuracy without being affected by the interference of reflected light, the color tone of the color filter, etc.
Preferably, the wavelength or the frequency, at which the spectrum has the minimum or maximum value, is in the visible light region. When the detection value is in the visible light region, the measurement becomes easier, and the cell thickness d can be detected with higher accuracy.
In addition, preferably, a light source of light which is transmitted along the light path has an emission spectrum which is continuous in at least a wavelength region corresponding to the detection value. When a light source having an emission spectrum which is continuous at a wavelength region corresponding to the detection value is used, the influence of the emission spectrum on the detection value can be reduced, and the cell thickness can be detected with higher accuracy. Halogen lamps are an example of such a light source that has an emission spectrum which is continuous in the visible light region, and fluorescent tubes are an example of such a light source that has an emission spectrum which is not continuous in the visible light region.
According to another aspect of the present invention, a cell thickness control system for controlling a cell thickness of a liquid crystal panel which is constructed by laminating two substrates and disposing a liquid crystal layer between the substrates includes a compressing means for applying a controlled pressure to the liquid crystal panel; an optical detection system including a light path for transmitting light through a first polarizing means, the liquid crystal layer, and a second polarizing means, in that order; a spectrum obtaining unit for obtaining a spectrum of light which is emitted from the optical detection system; a detection value deriving means for deriving a detection value which is a wavelength, a frequency, or other value related to the wavelength or the frequency at which the spectrum has a minimum or maximum value; and a controlling means for controlling the pressure of the compressing means so that the detection value becomes closer to a value corresponding to a desired value of the cell thickness.
Preferably, the controlling means controls the pressure of the compressing means based on a predetermined relationship between the pressure applied on the liquid crystal panel and the change in the detection value or of the cell thickness corresponding to the detection value. Accordingly, the cell thickness can be controlled with higher accuracy in a shorter time. In this case, the relationship between the pressure and the change in the detection value or of the cell thickness corresponding to the detection value around the desired value of the cell thickness is preferably used.
In addition, preferably, the compressing means includes a pair of clamping members, at least one of which is transparent, and which oppose each other with the liquid crystal panel therebetween, a sealing means for sealing gaps between the clamping members and the liquid crystal panel, and a fluid supplying means for supplying a fluid to the gaps between the clamping members and the liquid crystal panel with the controlled pressure. By disposing the liquid crystal panel between the clamping members and applying the pressure on the liquid crystal panel via the fluid supplied to the gaps between the clamping members and the liquid crystal panel, the liquid crystal panel can be uniformly and flexibly compressed. Thus, the cell thickness can be controlled with higher accuracy and adjustments can be performed more precisely, so that the time required for controlling the cell thickness can be reduced compared with the conventional methods.
In addition, according to another aspect of the present invention, a manufacturing method for a liquid crystal device including a liquid crystal panel which is constructed by laminating two substrates and disposing a liquid crystal layer between the substrates includes the steps of setting a light path for transmitting light through a first polarizing means, the liquid crystal layer, and a second polarizing means, in that order; obtaining a spectrum of light which is transmitted along the light path; deriving a detection value which is a wavelength, a frequency, or other value related to the wavelength or the frequency at which the spectrum has the minimum or maximum value; and compressing the liquid crystal panel in accordance with the detection value and making adjustments so that the detection value becomes almost the same as a value corresponding to a desired value of the cell thickness.
Preferably, a liquid crystal is first injected into the liquid crystal panel, and is then sealed in such a state that the liquid crystal panel is compressed in accordance with the detection value and adjustments are made so that the detection value becomes almost the same as the value corresponding to the desired value of the cell thickness.
In addition, according to another aspect of the present invention, a cell thickness detection method for detecting a cell thickness of a liquid crystal panel which is constructed by disposing two substrates in such a manner that the substrates oppose each other and disposing a liquid crystal layer between the substrates includes the steps of setting a light path for transmitting light through a first polarizing means, the liquid crystal layer, and a second polarizing means, in that order; obtaining a spectrum of light which is transmitted along the light path; deriving a detection value which is a wavelength or a frequency at which the spectrum has the minimum or maximum value; and determining the cell thickness based on the detection value.
In addition, according to another aspect of the present invention, a cell thickness detection method for detecting a cell thickness of a liquid crystal panel which is constructed by disposing two substrates in such a manner that the substrates oppose each other and disposing a liquid crystal layer between the substrates includes the steps of setting a light path for transmitting light through a first polarizing means, the liquid crystal layer, and a second polarizing means, in that order; obtaining a spectrum of light which is transmitted along the light path; deriving a detection value which is a value corresponding to a wavelength or a frequency at which the spectrum has the minimum or maximum value; and determining the cell thickness based on the detection value.